DESCRIPTION: P.I. proposes to continue and extend his studies of the circadian visual system, i.e. neuroanatomical substrate of the effects of light of circadian rhythms. The proposal has three general aims: The first is to understand the role serotonergic system as a modulator of circadian rhythmicity. This series of studies will combine electrical stimulation and pharmacological techniques to evaluate (a) circadian phase control by the ascending serotonergic system, (b) inhibitory control of the circadian rhythms phase response to light by the ascending serotonergic system and (c) elucidation of whether the dorsal or median raphe nuclei are involved in circadian rhythm regulation. The second is directed towards the elucidation of the relationship between serotonergic system and the photoconduction of FOS-protein by SCN or intergeniculate leaflet (IGL) cells. Experiments will be conducted which evaluate (a) the ability of serotonin system activation to block FOS protein induction in SCN or IGL neurons and (b) whether it is the dorsal or median raphe nucleus that controls the serotonergic activity in the SCN and IGL. The third group of experiments will investigate the possibility that the PLi - the posterior limitans thalamic nucleus is a "new" part of the circadian visual system. The hypothesis here arises out of observations that the IGL is anatomical connected with the PLi, and continued investigations of IGL efferent and afferent anatomy are planned. P.I. will study (a) the IGL's relationship to the PLi, (b) the sites of retina input to the PLi, (c) the efferent/afferent relationship between the IGL and superior colliculus, and (d) the circadian rhythm function of the PLi.